Median AQI
37
Good
Wisconsin · County air quality · 2025
Grant County, Wisconsin
Median AQI 37 (Good). 72.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 72.4%
- Good-air days
- 0
- Unhealthy days
- 36%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Grant County's air is good on balance, more polluted than the median US county, a median AQI of 37 with 72.4% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 37
- median AQI · Good
- 72.4%
- days rated Good
- PM2.5
- main pollutant
- 36%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 119.
Data updated July 2026
- Good · 131 d · 72.4%
- Moderate · 49 d · 27.1%
- USG · 1 d · 0.6%
How did Grant County's air break down in 2025?
Across 181 monitored days, 131 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 119 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 37 (Good).
Insights: Grant County, Wisconsin. EPA monitors recorded a median Air Quality Index of 37 across 181 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 131 (72%) fell in the Good band (AQI 0–50), 49 (27%) registered Moderate readings, and 1 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 65, while the worst single-day peak hit 119 (USG). Residents averaged about 21.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (181 days). Across the 2020–2025 trend window, good days shifted by -104 and the median AQI moved -3 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 119, usg but never Unhealthy. Nearby counties show comparable readings: Ashland (85.6% good, AQI 39); Brown (79.0% good, AQI 37); Columbia (84.6% good, AQI 42); Dane (71.8% good, AQI 40); Dodge (76.4% good, AQI 39); Door (85.7% good, AQI 40).
Air Quality Summary
Good Days
72.4%
131 of 181 monitored days
-2.6pp vs 75% target
Max AQI Recorded
119
USG
Health Grade
Moderate
90th-pct AQI 65
Grant County, Good days share 72.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Grant County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 181 monitored days across EPA AQI categories.
Good
131
72%
Moderate
49
27%
USG
1
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Grant County.
- PM2.5 · 181 days · 100.0%
Health Impact Assessment
Moderate
Grant County's air quality is rated Moderate based on 72.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 72.4% of monitored days in 2025, with a median AQI of 37. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 181 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Grant County. Best year: 2024 (263 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 235 | 126 | 0 | 0 | 40 | 84 |
| 2021 | 200 | 155 | 0 | 0 | 46 | 96 |
| 2022 | 241 | 118 | 0 | 0 | 39 | 80 |
| 2023 | 198 | 160 | 4 | 2 | 48 | 221 |
| 2024 | 263 | 103 | 0 | 0 | 36 | 82 |
| 2025 | 131 | 49 | 1 | 0 | 37 | 119 |
How does Grant County compare?
How Grant County compares
Good-day share worse than US avg
Grant County 72.4%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI better than US avg
Grant County 37
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Grant County 0
Ashland County, Wisconsin 1
US average 0
Other Counties in Wisconsin
Air quality comparison for nearby counties in Wisconsin.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Grant County.
Alachua County, Florida
AQI 37 · 90.1% good
Beltrami County, Minnesota
AQI 37 · 88.8% good
Benewah County, Idaho
AQI 37 · 74.6% good
Brevard County, Florida
AQI 37 · 89.7% good
Brown County, Indiana
AQI 37 · 94.5% good
Brown County, Wisconsin
AQI 37 · 79.0% good
What Grant County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 37 means for exposure. Health guidance
- See how Grant County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Grant County with its Wisconsin neighbours before drawing a conclusion about the region. All of Wisconsin
Based on 181 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Grant County, Wisconsin? ▼
Grant County has a median Air Quality Index (AQI) of 37, rated "Good." 72.4% of monitored days (131 out of 181) had good air quality in 2025.
What is the main pollutant in Grant County? ▼
The primary pollutant in Grant County is Fine Particles (PM2.5), which was the main AQI driver on 181 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Grant County have? ▼
In 2025, Grant County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 119.
Is the air quality in Grant County getting better or worse? ▼
Air quality in Grant County is improving based on 5-year trends (2020-2025). Best year: 2024 with 263 good days. Worst year: 2025 with 131 good days.
What does AQI 37 mean for health? ▼
Grant County's median AQI of 37 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Grant County compare to other counties in Wisconsin? ▼
Grant County has 72.4% good air days. Nearby counties in Wisconsin: Ashland (85.6% good), Brown (79.0% good), Columbia (84.6% good), Dane (71.8% good), Dodge (76.4% good), Door (85.7% good).
What is the 90th percentile AQI in Grant County? ▼
The 90th percentile AQI for Grant County is 65, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 119 (USG).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.